RFID systems with session-dependent replies

ABSTRACT

RFID systems may be configured to use session-dependent replies. When an RFID tag is involved in a certain inventorying session, the tag may respond to inventorying commands with a reply that is at least partly generated based on the session. For example, the tag may generate a reply with a string that has parity based on the session or includes an identifier for the session. The string may be a random number, a tag identifier or item identifier, or any other suitable data sent from the tag.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. Nos. 62/554,657 and 62/554,986, both filed on Sep. 6,2017. The disclosures of the above applications are hereby incorporatedby reference for all purposes.

BACKGROUND

Radio-Frequency Identification (RFID) systems typically include RFIDreaders, also known as RFID reader/writers or RFID interrogators, andRFID tags. RFID systems can be used in many ways for locating andidentifying objects to which the tags are attached. RFID systems areuseful in product-related and service-related industries for trackingobjects being processed, inventoried, or handled. In such cases, an RFIDtag is usually attached to an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to inventoryone or more RFID tags, where inventorying involves singulating a tag,receiving an identifier from a tag, and/or acknowledging a receivedidentifier (e.g., by transmitting an acknowledge command). “Singulated”is defined as a reader singling-out one tag, potentially from amongmultiple tags, for a reader-tag dialog. “Identifier” is defined as anumber identifying the tag or the item to which the tag is attached,such as a tag identifier (TID), electronic product code (EPC), etc. Thereader transmitting a Radio-Frequency (RF) wave performs theinterrogation. The RF wave is typically electromagnetic, at least in thefar field. The RF wave can also be predominantly electric or magnetic inthe near or transitional near field. The RF wave may encode one or morecommands that instruct the tags to perform one or more actions.

In typical RFID systems, an RFID reader transmits a modulated RFinventory signal (a command), receives a tag reply, and transmits an RFacknowledgement signal responsive to the tag reply. A tag that sensesthe interrogating RF wave may respond by transmitting back another RFwave. The tag either generates the transmitted back RF wave originally,or by reflecting back a portion of the interrogating RF wave in aprocess known as backscatter. Backscatter may take place in a number ofways.

The reflected-back RF wave may encode data stored in the tag, such as anumber. The response is demodulated and decoded by the reader, whichthereby identifies, counts, or otherwise interacts with the associateditem. The decoded data can denote a serial number, a price, a date, atime, a destination, an encrypted message, an electronic signature,other attribute(s), any combination of attributes, and so on.Accordingly, when a reader receives tag data it can learn about the itemthat hosts the tag and/or about the tag itself.

An RFID tag typically includes an antenna section, a radio section, apower-management section, and frequently a logical section, a memory, orboth. In some RFID tags the power-management section included an energystorage device such as a battery. RFID tags with an energy storagedevice are known as battery-assisted, semi-active, or active tags. OtherRFID tags can be powered solely by the RF signal they receive. Such RFIDtags do not include an energy storage device and are called passivetags. Of course, even passive tags typically include temporary energy-and data/flag-storage elements such as capacitors or inductors.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

Embodiments are directed to RFID systems that use session-dependentreplies. When an RFID tag is involved in a certain inventorying session,the tag may respond to inventorying commands with a reply that is atleast partly generated based on the identity of the inventoryingsession. For example, the tag may generate a reply with a string thathas parity based on the session or includes an identifier for thesession. The string may be a random number, a tag identifier or itemidentifier, or any other suitable data sent from the tag.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the foregoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of aspects as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1.

FIG. 3 is a conceptual diagram for explaining a half-duplex mode ofcommunication between the components of the RFID system of FIG. 1.

FIG. 4 is a block diagram showing a detail of an RFID tag, such as theone shown in FIG. 2.

FIGS. 5A and 5B illustrate signal paths during tag-to-reader andreader-to-tag communications in the block diagram of FIG. 4.

FIG. 6 is a block diagram showing a detail of an RFID reader system,such as the one shown in FIG. 1.

FIG. 7 is a block diagram illustrating an overall architecture of anRFID system according to embodiments.

FIG. 8 depicts a portion of a tag inventorying process.

FIG. 9 depicts how a reader may acknowledge a tag responding to adifferent reader.

FIG. 10 depicts how inventorying-session-dependent replies can be usedto prevent a reader from acknowledging a tag responding to a differentreader.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments or examples. These embodimentsor examples may be combined, other aspects may be utilized, andstructural changes may be made without departing from the spirit orscope of the present disclosure. The following detailed description istherefore not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

As used herein, “memory” is one of ROM, RAM, SRAM, DRAM, NVM, EEPROM,FLASH, Fuse, MRAM, FRAM, and other similar volatile and nonvolatileinformation-storage technologies as will be known to those skilled inthe art. Some portions of memory may be writeable and some not.“Command” refers to a reader request for one or more tags to perform oneor more actions, and includes one or more tag instructions preceded by acommand identifier or command code that identifies the command and/orthe tag instructions. “Instruction” refers to a request to a tag toperform a single explicit action (e.g., write data into memory).“Program” refers to a request to a tag to perform a set or sequence ofinstructions (e.g., read a value from memory and, if the read value isless than a threshold then lock a memory word). “Protocol” refers to anindustry standard for communications between a reader and a tag (andvice versa), such as the Class-1 Generation-2 UHF RFID Protocol forCommunications at 860 MHz-960 MHz by GS1 EPCglobal, Inc. (“Gen2Specification”), versions 1.2.0 and 2.0 of which are hereby incorporatedby reference.

In some RFID systems, a reader and tag communicate using an inventoryingprocess. According to one example inventorying process, such as the onedescribed in the Gen2 Specification, a reader transmits a query command(e.g., a Gen2 Query, QueryAdj, or QueryRep command) that instructs tagsthat meet certain criteria to respond. Upon receiving the command, a tagthat meets the criteria responds with a random or pseudorandom number.The reader, upon receiving the tag response, transmits anacknowledgement command incorporating the random/pseudorandom number.When the tag receives the acknowledgement command and determines thatthe incorporated number is identical to the number it previously sent,the tag responds with additional information, such as a tag or itemidentifier, or any other suitable information.

The Gen2 Specification provides multiple inventorying sessions to allowmultiple readers to independently inventory a common tag population.When transmitting a query command, a reader can specify a particularinventory session and optionally a particular session flag value. Tagsthat have the appropriate session flag value for the specified inventorysession may then respond.

In situations where multiple readers are inventorying in multiplesessions, a reader inventorying in a first session may receive a randomnumber sent by a tag being inventoried in a second, different session.The reader may then mistakenly attempt to inventory the tag, which canbe problematic. In some embodiments, such mistaken inventorying attemptscan be addressed using session-dependent replies.

FIG. 1 is a diagram of the components of a typical RFID system 100,incorporating embodiments. An RFID reader 110 transmits an interrogatingRF signal 112. RFID tag 120 in the vicinity of RFID reader 110 sensesinterrogating RF signal 112 and generates signal 126 in response. RFIDreader 110 senses and interprets signal 126. The signals 112 and 126 mayinclude RF waves and/or non-propagating RF signals (e.g., reactivenear-field signals).

Reader 110 and tag 120 communicate via signals 112 and 126. Whencommunicating, each encodes, modulates, and transmits data to the other,and each receives, demodulates, and decodes data from the other. Thedata can be modulated onto, and demodulated from, RF waveforms. The RFwaveforms are typically in a suitable range of frequencies, such asthose near 900 MHz, 13.56 MHz, and so on.

The communication between reader and tag uses symbols, also called RFIDsymbols. A symbol can be a delimiter, a calibration value, and so on.Symbols can be implemented for exchanging binary data, such as “0” and“1”, if that is desired. When symbols are processed by reader 110 andtag 120 they can be treated as values, numbers, and so on.

Tag 120 can be a passive tag, or an active or battery-assisted tag(i.e., a tag having its own power source). When tag 120 is a passivetag, it is powered from signal 112.

FIG. 2 is a diagram of an RFID tag 220, which may function as tag 120 ofFIG. 1. Tag 220 is drawn as a passive tag, meaning it does not have itsown power source. Much of what is described in this document, however,applies also to active and battery-assisted tags.

Tag 220 is typically (although not necessarily) formed on asubstantially planar inlay 222, which can be made in many ways known inthe art. Tag 220 includes a circuit which may be implemented as an IC224. In some embodiments IC 224 is implemented in complementarymetal-oxide semiconductor (CMOS) technology. In other embodiments IC 224may be implemented in other technologies such as bipolar junctiontransistor (BJT) technology, metal-semiconductor field-effect transistor(MESFET) technology, and others as will be well known to those skilledin the art. IC 224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is often flat and attached to inlay 222. IC224 is electrically coupled to the antenna via suitable IC contacts (notshown in FIG. 2). The term “electrically coupled” as used herein maymean a direct electrical connection, or it may mean a connection thatincludes one or more intervening circuit blocks, elements, or devices.The “electrical” part of the term “electrically coupled” as used in thisdocument shall mean a coupling that is one or more of ohmic/galvanic,capacitive, and/or inductive. Similarly, the terms “electricallyisolated” or “electrically decoupled” as used herein mean thatelectrical coupling of one or more types (e.g., galvanic, capacitive,and/or inductive) is not present, at least to the extent possible. Forexample, elements that are electrically isolated from each other aregalvanically isolated from each other, capacitively isolated from eachother, and/or inductively isolated from each other. Of course,electrically isolated components will generally have some unavoidablestray capacitive or inductive coupling between them, but the intent ofthe isolation is to minimize this stray coupling to a negligible levelwhen compared with an electrically coupled path.

IC 224 is shown with a single antenna port, comprising two IC contactselectrically coupled to two antenna segments 226 and 228 which are shownhere forming a dipole. Many other embodiments are possible using anynumber of ports, contacts, antennas, and/or antenna segments.

Diagram 250 depicts top and side views of tag 252, formed using a strap.Tag 252 differs from tag 220 in that it includes a substantially planarstrap substrate 254 having strap contacts 256 and 258. IC 224 is mountedon strap substrate 254 such that the IC contacts on IC 224 electricallycouple to strap contacts 256 and 258 via suitable connections (notshown). Strap substrate 254 is then placed on inlay 222 such that strapcontacts 256 and 258 electrically couple to antenna segments 226 and228. Strap substrate 254 may be affixed to inlay 222 via pressing, aninterface layer, one or more adhesives, or any other suitable means.

Diagram 260 depicts a side view of an alternative way to place strapsubstrate 254 onto inlay 222. Instead of strap substrate 254's surface,including strap contacts 256/258, facing the surface of inlay 222, strapsubstrate 254 is placed with its strap contacts 256/258 facing away fromthe surface of inlay 222. Strap contacts 256/258 can then be eithercapacitively coupled to antenna segments 226/228 through strap substrate254, or conductively coupled using a through-via which may be formed bycrimping strap contacts 256/258 to antenna segments 226/228. In someembodiments, the positions of strap substrate 254 and inlay 222 may bereversed, with strap substrate 254 mounted beneath inlay 222 and strapcontacts 256/258 electrically coupled to antenna segments 226/228through inlay 222. Of course, in yet other embodiments strap contacts256/258 may electrically couple to antenna segments 226/228 through bothinlay 222 and strap substrate 254.

In operation, the antenna receives a signal and communicates it to IC224, which may both harvest power and respond if appropriate, based onthe incoming signal and the IC's internal state. If IC 224 usesbackscatter modulation then it responds by modulating the antenna'sreflectance, which generates response signal 126 from signal 112transmitted by the reader. Electrically coupling and uncoupling the ICcontacts of IC 224 can modulate the antenna's reflectance, as canvarying the admittance of a shunt-connected circuit element which iscoupled to the IC contacts. Varying the impedance of a series-connectedcircuit element is another means of modulating the antenna'sreflectance. If IC 224 is capable of transmitting signals (e.g., has itsown power source, is coupled to an external power source, and/or is ableto harvest sufficient power to transmit signals), then IC 224 mayrespond by transmitting response signal 126.

In the embodiments of FIG. 2, antenna segments 226 and 228 are separatefrom IC 224. In other embodiments, the antenna segments mayalternatively be formed on IC 224. Tag antennas according to embodimentsmay be designed in any form and are not limited to dipoles. For example,the tag antenna may be a patch, a slot, a loop, a coil, a horn, aspiral, a monopole, microstrip, stripline, or any other suitableantenna.

An RFID tag such as tag 220 is often attached to or associated with anindividual item or the item packaging. An RFID tag may be fabricated andthen attached to the item or packaging, or may be partly fabricatedbefore attachment to the item or packaging and then completelyfabricated upon attachment to the item or packaging. In someembodiments, the manufacturing process of the item or packaging mayinclude the fabrication of an RFID tag. In these embodiments, theresulting RFID tag may be integrated into the item or packaging, andportions of the item or packaging may serve as tag components. Forexample, conductive item or packaging portions may serve as tag antennasegments or contacts. Nonconductive item or packaging portions may serveas tag substrates or inlays. If the item or packaging includesintegrated circuits or other circuitry, some portion of the circuitrymay be configured to operate as part or all of an RFID tag IC. An “RFIDIC” may refer to an item capable of receiving and responding to RFIDsignals. For example, an item having a separate but attached RFID tagcan be considered an RFID IC, as is an item having an integrated RFIDtag or an item manufactured to have the capabilities of an RFID tag. Astandalone RFID tag may also be referred to as an “RFID IC”.

The components of the RFID system of FIG. 1 may communicate with eachother in any number of modes. One such mode is called full duplex, whereboth reader 110 and tag 120 can transmit at the same time. In someembodiments, RFID system 100 may be capable of full duplex communicationif tag 120 is configured to transmit signals as described above. Anothersuch mode, suitable for passive tags, is called half-duplex, and isdescribed below.

FIG. 3 is a conceptual diagram 300 for explaining half-duplexcommunications between the components of the RFID system of FIG. 1, inthis case with tag 120 implemented as passive tag 220 of FIG. 2. Theexplanation is made with reference to a TIME axis, and also to a humanmetaphor of “talking” and “listening”. The actual technicalimplementations for “talking” and “listening” are now described.

RFID reader 110 and RFID tag 120 talk and listen to each other by takingturns. As seen on axis TIME, when reader 110 talks to tag 120 thecommunication session is designated as “R→T”, and when tag 120 talks toreader 110 the communication session is designated as “T→R”. Along theTIME axis, a sample R→T communication session occurs during a timeinterval 312, and a following sample T→R communication session occursduring a time interval 326. Interval 312 may typically be of a differentduration than interval 326—here the durations are shown approximatelyequal only for purposes of illustration.

According to blocks 332 and 336, RFID reader 110 talks during interval312, and listens during interval 326. According to blocks 342 and 346,RFID tag 120 listens while reader 110 talks (during interval 312), andtalks while reader 110 listens (during interval 326).

In terms of actual behavior, during interval 312 reader 110 talks to tag120 as follows. According to block 352, reader 110 transmits signal 112,which was first described in FIG. 1. At the same time, according toblock 362, tag 120 receives signal 112 and processes it to extract dataand so on. Meanwhile, according to block 372, tag 120 does notbackscatter with its antenna, and according to block 382, reader 110 hasno signal to receive from tag 120.

During interval 326, which may also be referred to as a backscatter timeinterval or backscatter interval, tag 120 talks to reader 110 asfollows. According to block 356, reader 110 transmits a Continuous Wave(CW) signal, which can be thought of as a carrier that typically encodesno information. This CW signal serves both to transfer energy to tag 120for its own internal power needs, and also as a carrier that tag 120 canmodulate with its backscatter. Indeed, during interval 326, according toblock 366, tag 120 does not receive a signal for processing. Instead,according to block 376, tag 120 modulates the CW emitted according toblock 356 so as to generate backscatter signal 126, for example byadjusting its antenna reflectance. Concurrently, according to block 386,reader 110 receives backscatter signal 126 and processes it.

FIG. 4 is a block diagram showing a detail of an RFID IC, such as IC 224in FIG. 2. Electrical circuit 424 in FIG. 4 may be formed in an IC of anRFID tag, such as tag 220 of FIG. 2. Circuit 424 has a number of maincomponents that are described in this document. Circuit 424 may have anumber of additional components from what is shown and described, ordifferent components, depending on the exact implementation.

Circuit 424 shows two IC contacts 432, 433, suitable for coupling toantenna segments such as antenna segments 226/228 of RFID tag 220 ofFIG. 2. When two IC contacts form the signal input from and signalreturn to an antenna they are often referred-to as an antenna port. ICcontacts 432, 433 may be made in any suitable way, such as from metallicpads and so on. In some embodiments circuit 424 uses more than two ICcontacts, especially when tag 220 has more than one antenna port and/ormore than one antenna.

Circuit 424 includes signal-routing section 435 which may include signalwiring, signal-routing busses, receive/transmit switches, and so on thatcan route a signal to the components of circuit 424. In some embodimentsIC contacts 432/433 couple galvanically and/or inductively tosignal-routing section 435. In other embodiments (such as is shown inFIG. 4) circuit 424 includes optional capacitors 436 and/or 438 which,if present, capacitively couple IC contacts 432/433 to signal-routingsection 435. This capacitive coupling causes IC contacts 432/433 to begalvanically decoupled from signal-routing section 435 and other circuitcomponents.

Capacitive coupling (and resultant galvanic decoupling) between ICcontacts 432 and/or 433 and components of circuit 424 is desirable incertain situations. For example, in some RFID tag embodiments ICcontacts 432 and 433 may galvanically connect to terminals of a tuningloop on the tag. In this situation, capacitors 436 and/or 438galvanically decouple IC contact 432 from IC contact 433, therebypreventing the formation of a short circuit between the IC contactsthrough the tuning loop.

Capacitors 436/438 may be implemented within circuit 424 and/or partlyor completely external to circuit 424. For example, a dielectric orinsulating layer on the surface of the IC containing circuit 424 mayserve as the dielectric in capacitor 436 and/or capacitor 438. Asanother example, a dielectric or insulating layer on the surface of atag substrate (e.g., inlay 222 or strap substrate 254) may serve as thedielectric in capacitors 436/438. Metallic or conductive layerspositioned on both sides of the dielectric layer (i.e., between thedielectric layer and the IC and between the dielectric layer and the tagsubstrate) may then serve as terminals of the capacitors 436/438. Theconductive layers may include IC contacts (e.g., IC contacts 432/433),antenna segments (e.g., antenna segments 226/228), or any other suitableconductive layers.

Circuit 424 also includes a rectifier and PMU (Power Management Unit)441 that harvests energy from the RF signal received by antenna segments226/228 to power the circuits of IC 424 during either or bothreader-to-tag (R→T) and tag-to-reader (T→R) sessions. Rectifier and PMU441 may be implemented in any way known in the art, and may include oneor more components configured to convert an alternating-current (AC) ortime-varying signal into a direct-current (DC) or substantiallytime-invariant signal.

Circuit 424 additionally includes a demodulator 442 that demodulates theRF signal received via IC contacts 432, 433. Demodulator 442 may beimplemented in any way known in the art, for example including a slicer,an amplifier, and so on.

Circuit 424 further includes a processing block 444 that receives theoutput from demodulator 442 and performs operations such as commanddecoding, memory interfacing, and so on. In addition, processing block444 may generate an output signal for transmission. Processing block 444may be implemented in any way known in the art, for example bycombinations of one or more of a processor, memory, decoder, encoder,and so on.

Circuit 424 additionally includes a modulator 446 that modulates anoutput signal generated by processing block 444. The modulated signal istransmitted by driving IC contacts 432, 433, and therefore driving theload presented by the coupled antenna segment or segments. Modulator 446may be implemented in any way known in the art, for example including aswitch, driver, amplifier, and so on.

In one embodiment, demodulator 442 and modulator 446 may be combined ina single transceiver circuit. In another embodiment modulator 446 maymodulate a signal using backscatter. In another embodiment modulator 446may include an active transmitter. In yet other embodiments demodulator442 and modulator 446 may be part of processing block 444.

Circuit 424 additionally includes a memory 450 to store data 452. Atleast a portion of memory 450 is preferably implemented as a nonvolatilememory (NVM), which means that data 452 is retained even when circuit424 does not have power, as is frequently the case for a passive RFIDtag.

In some embodiments, particularly in those with more than one antennaport, circuit 424 may contain multiple demodulators, rectifiers, PMUs,modulators, processing blocks, and/or memories.

In terms of processing a signal, circuit 424 operates differently duringa R→T session and a T→R session. The different operations are describedbelow, in this case with circuit 424 representing an IC of an RFID tag.

FIG. 5A shows version 524-A of components of circuit 424 of FIG. 4,further modified to emphasize a signal operation during a R→T sessionduring time interval 312 of FIG. 3. Demodulator 442 demodulates an RFsignal received from IC contacts 432, 433. The demodulated signal isprovided to processing block 444 as C_IN. In one embodiment, C_IN mayinclude a received stream of symbols.

Version 524-A shows as relatively obscured those components that do notplay a part in processing a signal during a R→T session. Rectifier andPMU 441 may be active, such as for converting RF power. Modulator 446generally does not transmit during a R→T session, and typically does notinteract with the received RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples modulator 446 fromthe RF signal, or by designing modulator 446 to have a suitableimpedance, and so on.

Although modulator 446 is typically inactive during a R→T session, itneed not be so. For example, during a R→T session modulator 446 could beadjusting its own parameters for operation in a future session, and soon.

FIG. 5B shows version 524-B of components of circuit 424 of FIG. 4,further modified to emphasize a signal operation during a T→R sessionduring time interval 326 of FIG. 3. Processing block 444 outputs asignal C_OUT. In one embodiment, C_OUT may include a stream of symbolsfor transmission. Modulator 446 then modulates C_OUT and provides it toantenna segments such as segments 226/228 of RFID tag 220 via ICcontacts 432, 433.

Version 524-B shows as relatively obscured those components that do notplay a part in processing a signal during a T→R session. Rectifier andPMU 441 may be active, such as for converting RF power. Demodulator 442generally does not receive during a T→R session, and typically does notinteract with the transmitted RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples demodulator 442 fromthe RF signal, or by designing demodulator 442 to have a suitableimpedance, and so on.

Although demodulator 442 is typically inactive during a T→R session, itneed not be so. For example, during a T→R session demodulator 442 couldbe adjusting its own parameters for operation in a future session, andso on.

In typical embodiments, demodulator 442 and modulator 446 are operableto demodulate and modulate signals according to a protocol, such as theGen2 Specification mentioned above. In embodiments where circuit 424includes multiple demodulators and/or modulators, each may be configuredto support different protocols or different sets of protocols. Aprotocol specifies, in part, symbol encodings, and may include a set ofmodulations, rates, timings, or any other parameter associated with datacommunications. In addition, a protocol can be a variant of a statedspecification such as the Gen2 Specification, for example includingfewer or additional commands than the stated specification calls for,and so on. In such instances, additional commands are sometimes calledcustom commands.

FIG. 6 is a block diagram of an RFID reader system 600 according toembodiments. RFID reader system 600 includes a local block 610, andoptionally remote components 670. Local block 610 and remote components670 can be implemented in any number of ways. For example, local block610 or portions of local block 610 may be implemented as a standalonedevice or as a component in another device. In some embodiments, localblock 610 or portions of local block 610 may be implemented as a mobiledevice, such as a handheld RFID reader, or as a component in a mobiledevice, such as a laptop, tablet, smartphone, wearable device, or anyother suitable mobile device. It will be recognized that RFID reader 110of FIG. 1 is the same as local block 610, if remote components 670 arenot provided. Alternately, RFID reader 110 can be implemented instead byRFID reader system 600, of which only the local block 610 is shown inFIG. 1.

In some embodiments, one or more of the blocks or components of readersystem 600 may be implemented as integrated circuits. For example, localblock 610, one or more of the components of local block 610, and/or oneor more of the remote component 670 may be implemented as integratedcircuits using CMOS technology, BJT technology, MESFET technology,and/or any other suitable implementation technology.

Local block 610 is responsible for communicating with RFID tags. Localblock 610 includes a block 651 of an antenna and a driver of the antennafor communicating with the tags. Some readers, like that shown in localblock 610, contain a single antenna and driver. Some readers containmultiple antennas and drivers and a method to switch signals among them,including sometimes using different antennas for transmitting and forreceiving. Some readers contain multiple antennas and drivers that canoperate simultaneously. In some embodiments, block 651 may be aphased-array antenna or synthesized-beam antenna (SBA), and local block610 may be implemented in a synthesized-beam reader (SBR) configured togenerate one or more beams via the SBA. A demodulator/decoder block 653demodulates and decodes backscattered waves received from the tags viaantenna/driver block 651. Modulator/encoder block 654 encodes andmodulates an RF wave that is to be transmitted to the tags viaantenna/driver block 651.

Local block 610 additionally includes an optional local processor 656.Local processor 656 may be implemented in any number of ways known inthe art. Such ways include, by way of examples and not of limitation,digital and/or analog processors such as microprocessors anddigital-signal processors (DSPs); controllers such as microcontrollers;software running in a machine such as a general purpose computer;programmable circuits such as Field Programmable Gate Arrays (FPGAs),Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices(PLDs), Application Specific Integrated Circuits (ASIC), any combinationof one or more of these; and so on. In some cases, some or all of thedecoding function in block 653, the encoding function in block 654, orboth, may be performed instead by local processor 656. In some cases,local processor 656 may implement an encryption or authenticationfunction; in some cases, one or more of these functions can bedistributed among other blocks such as encoding block 654, or may beentirely incorporated in another block.

Local block 610 additionally includes an optional local memory 657.Local memory 657 may be implemented in any number of ways known in theart, including, by way of example and not of limitation, any of thememory types described above as well as any combination thereof. Localmemory 657 can be implemented separately from local processor 656, or inan IC with local processor 656, with or without other components. Localmemory 657, if provided, can store programs for local processor 656 torun, if needed.

In some embodiments, local memory 657 stores data read from tags, ordata to be written to tags, such as Electronic Product Codes (EPCs), TagIdentifiers (TIDs) and other data. Local memory 657 can also includereference data that is to be compared to EPCs, instructions and/or rulesfor how to encode commands for the tags, modes for controlling antenna651, encryption/authentication algorithms, algorithms for tracking taglocation or movement, secret keys, key pairs, individual public and/orprivate keys, electronic signatures, and so on. In some of theseembodiments, local memory 657 is provided as a database.

Some components of local block 610 typically treat the data as analog,such as the antenna/driver block 651. Other components such as localmemory 657 typically treat the data as digital. At some point, there isa conversion between analog and digital. Based on where this conversionoccurs, a reader may be characterized as “analog” or “digital”, but mostreaders contain a mix of analog and digital functionality.

If remote components 670 are provided, they are coupled to local block610 via an electronic communications network 680. Network 680 can be aLocal Area Network (LAN), a Metropolitan Area Network (MAN), a Wide AreaNetwork (WAN), a network of networks such as the internet, or a localcommunication link, such as a USB, PCI, and so on. Local block 610 mayinclude a local network connection 659 for communicating withcommunications network 680 or may couple to a separate device orcomponent configured to communicate with communications network 680.Communications on the network can be secure, such as if they areencrypted or physically protected, or insecure if they are not encryptedor otherwise protected.

There can be one or more remote component(s) 670. If more than one, theycan be located at the same location, or in different locations. They maycommunicate with each other and local block 610 via communicationsnetwork 680, or via other similar networks, and so on. Accordingly,remote component(s) 670 can use respective remote network connections.Only one such remote network connection 679 is shown, which is similarto local network connection 659, etc. In some embodiments, a single oneof the remote component(s) 670 may be configured to communicate withand/or control multiple local blocks, each similar to local block 610.

Remote component(s) 670 can also include a remote processor 676. Remoteprocessor 676 can be made in any way known in the art, such as wasdescribed with reference to local processor 656. Remote processor 676may also implement an encryption/authentication function and/or a taglocation/tracking function, similar to local processor 656.

Remote component(s) 670 can also include a remote memory 677. Remotememory 677 can be made in any way known in the art, such as wasdescribed with reference to local memory 657. Remote memory 677 mayinclude a local database, and a different database of a standardsorganization, such as one that can reference EPCs. Remote memory 677 mayalso contain information associated with commands, tag profiles, keys,or the like, similar to local memory 657.

One or more of the above-described elements may be combined anddesignated as operational processing block 690. Operational processingblock 690 includes those components that are provided of the following:local processor 656, remote processor 676, local network connection 659,remote network connection 679, and by extension an applicable portion ofcommunications network 680 that links remote network connection 679 withlocal network connection 659. The portion can be dynamically changeable,etc. In addition, operational processing block 690 can receive anddecode RF waves received via antenna/driver 651, and causeantenna/driver 651 to transmit RF waves according to what it hasprocessed.

Operational processing block 690 includes either local processor 656, orremote processor 676, or both. If both are provided, remote processor676 can be made such that it operates in a way complementary with thatof local processor 656. In fact, the two can cooperate. It will beappreciated that operational processing block 690, as defined this way,is in communication with both local memory 657 and remote memory 677, ifboth are present.

Accordingly, operational processing block 690 is location independent,in that its functions can be implemented either by local processor 656,or by remote processor 676, or by a combination of both. Some of thesefunctions are preferably implemented by local processor 656, and some byremote processor 676. Operational processing block 690 accesses localmemory 657, or remote memory 677, or both for storing and/or retrievingdata.

RFID reader system 600 operates by operational processing block 690generating communications for RFID tags. These communications areultimately transmitted by antenna/driver block 651, withmodulator/encoder block 654 encoding and modulating the information onan RF wave. Then data is received from the tags via antenna/driver block651, demodulated and decoded by demodulator/decoder block 653, andprocessed by operational processing block 690.

Embodiments of an RFID reader system can be implemented as hardware,software, firmware, or any combination. Such a system may be subdividedinto components or modules. Some of these components or modules can beimplemented as hardware, some as software, some as firmware, and some asa combination. An example of such a subdivision is now described,together with the RFID tag as an additional module.

FIG. 7 is a block diagram illustrating an overall architecture of anRFID system 700 according to embodiments. RFID system 700 may besubdivided into modules or components, each of which may be implementedby itself or in combination with others. In addition, some of them maybe present more than once. Other embodiments may be equivalentlysubdivided into different modules. Some aspects of FIG. 7 are parallelwith systems, modules, and components described previously.

An RFID tag 703 is considered here as a module by itself. RFID tag 703conducts a wireless communication 706 with the remainder, via the airinterface 705. Air interface 705 is really a boundary, in that signalsor data that pass through it are not intended to be transformed from onething to another. Specifications as to how readers and tags are tocommunicate with each other, for example the Gen2 Specification, alsoproperly characterize that boundary as an interface.

RFID system 700 includes one or more reader antennas 710, and an RFfront-end module 720 for interfacing with reader antenna(s) 710. Thesecan be made as described above.

RFID system 700 also includes a signal-processing module 730. In oneembodiment, signal-processing module 730 exchanges waveforms with RFfront-end module 720, such as I and Q waveform pairs.

RFID system 700 further includes a physical-driver module 740, which isalso known as a data-link module. In some embodiments, physical-drivermodule 740 exchanges bits with signal-processing module 730.Physical-driver module 740 can be the stage associated with the framingof data.

RFID system 700 additionally includes a media access control module 750.In one embodiment, media access control layer module 750 exchangespackets of bits with physical driver module 740. Media access controllayer module 750 can make decisions for sharing the medium of wirelesscommunication, which in this case is the air interface.

RFID system 700 moreover includes an application-programminglibrary-module 760. This module 760 can include application programminginterfaces (APIs), other objects, etc.

All of these RFID system functionalities can be supported by one or moreprocessors. One of these processors can be considered a host processor.Such a host processor might include a host operating system (OS) and/orcentral processing unit (CPU), as in module 770. In some embodiments,the processor is not considered as a separate module, but one thatincludes some of the above-mentioned modules of RFID system 700. In someembodiments, the one or more processors may perform operationsassociated with retrieving data that may include a tag public key, anelectronic signature, a tag identifier, an item identifier, and/or asigning-authority public key. In some embodiments, the one or moreprocessors may verify an electronic signature, create a tag challenge,and/or verify a tag response.

User interface module 780 may be coupled toapplication-programming-library module 760, for accessing the APIs. Userinterface module 780 can be manual, automatic, or both. It can besupported by the host OS/CPU module 770 mentioned above, or by aseparate processor, etc.

It will be observed that the modules of RFID system 700 form a chain.Adjacent modules in the chain can be coupled by appropriateinstrumentalities for exchanging signals. These instrumentalitiesinclude conductors, buses, interfaces, and so on. Theseinstrumentalities can be local, e.g. to connect modules that arephysically close to each other, or over a network, for remotecommunication.

The chain is used in one direction for receiving RFID waveforms and inthe other direction for transmitting RFID waveforms. In receiving mode,reader antenna(s) 710 receives wireless waves, which are in turnprocessed successively by the various modules in the chain. Processingcan terminate in any one of the modules. In transmitting mode, waveforminitiation can be in any one of the modules. Ultimately, signals arerouted to reader antenna(s) 710 to be transmitted as wireless waves.

The architecture of RFID system 700 is presented for purposes ofexplanation, and not of limitation. Its particular, subdivision intomodules need not be followed for creating embodiments. Furthermore, thefeatures of the present disclosure can be performed either within asingle one of the modules, or by a combination of them. In someembodiments RFID system 700 can be incorporated into another electronicdevice such as a checkout terminal in a store or a consumer device suchas a mobile phone.

RFID readers and tags can communicate using an inventorying process thatinvolves the exchange of information. FIG. 8 depicts a portion of a taginventorying process. At time 802, reader 810 transmits a query command(e.g., one of the Query/QueryRep/QueryAdj commands as described in theGen2 Specification) that specifies a particular session flag value forsession S1, or specifies the session S1. Tag 820, which happens to havethe appropriate session flag value for session S1, receives the querycommand, and at time 804 responds to the query command with a random (orpseudorandom) number RN. Reader 810 receives the RN, and at time 806transmits an acknowledge command (e.g., the ACK command as described inthe Gen2 Specification) containing the received RN. Tag 820 receives theacknowledge command containing the RN, and upon confirming that thereceived RN corresponds to the previously-sent RN, sends a reply toreader 810 at time 808. Subsequently, reader 810 and tag 820 maycontinue the communication as appropriate.

However, in some circumstances a reader inventorying in a first sessionmay overhear an RN that is part of an inventorying process in a secondsession and co-opt the inventorying process. FIG. 9 depicts how a readermay acknowledge a tag responding to a different reader. At time 902,reader 910 transmits a query command that specifies session S1 or aparticular session flag value for session S1. Also at time 902, reader912 transmits a query command that specifies session S2 or a particularsession flag value for session S2.

Tag 920 hears both query commands. However, as tag 920 only has theappropriate session flag value for session S1, at time 904 tag 920responds to the query command from reader 910 with a random number RN.

Although RN was meant for reader 910, reader 912 may also hear the RN.Reader 912 is also expecting to receive RNs from tags having theappropriate session flag value for session S2, and may determine thatthe RN sent from tag 920 is an RN from a tag having the appropriatesession flag value for session S2. Moreover, reader 910 may not haveheard the RN, or may be otherwise delayed and unable to transmit anacknowledge command before reader 912 transmits. Accordingly, at time906 reader 912 transmits an acknowledge command containing the receivedRN. Tag 920 receives the acknowledge command from reader 912, and uponconfirming that the contained RN corresponds to the previously-sent RN,sends a reply to reader 912 at time 908. As a result, reader 912 has nowco-opted the communication between reader 910 and tag 920.

One way to prevent the situation described in FIG. 9 is for tags torespond with session-dependent replies. FIG. 10 depicts howinventorying-session-dependent replies can be used to prevent a readerfrom acknowledging a tag responding to a different reader. At time 1002,reader 1010 transmits a query command that specifies session S1 or aparticular session flag value for session S1. Also at time 1002, reader1012 transmits a query command that specifies session S2 or a particularsession flag value for session S2.

Tag 1020 hears both query commands. However, as tag 1020 only has theappropriate session flag value for session S1, at time 1004 tag 1020responds to the query command from reader 1010 with a random numbergenerated based on session S1, denoted RN(S1).

Reader 1012 may hear RN(S1) even though it was intended for reader 1010.However, reader 1012 can determine that RN(S1) is meant for session S1,and because it was inventorying in session S2, reader 1012 will ignoreRN(S1). As a result, reader 1012 will not co-opt the communicationbetween reader 1010 and tag 1020.

In contrast, reader 1010 will not ignore RN(S1), because reader 1010 wasinventorying in session S1. Accordingly, at time 1006 reader 1010transmits an acknowledge command containing RN(S1). Tag 1020 receivesthe acknowledge command from reader 1010, and upon confirming that thecontained RN(S1) corresponds to the previously-sent RN(S1), sends areply to reader 1010 at time 1008. Subsequently, reader 1010 and tag1020 may continue the communication as appropriate.

A tag such as tag 1020 may generate RN(S1) or another suchsession-dependent string for a session-dependent reply in multiple ways.In some embodiments, the tag first generates a string and then uses anencoding scheme to adjust and impart session-dependency to the string,thereby creating an encoding-adjusted string from the generated string.In other embodiments, the tag may generate the string using an encodingscheme that imparts session-dependency. The tag may generate a stringalgorithmically (e.g., via the application of one or more algorithms toone or more input values), using a random or pseudorandom numbergenerator, by retrieving the string from tag IC memory, and/or via acombination of two or more techniques. Accordingly, the string mayinclude a random or pseudorandom number (e.g., an RN16 or tag handleaccording to the Gen2 Specification), a tag or item identifier, apointer to a remote location, an algorithmically generated value, acryptographic value (e.g., a value generated during a cryptographicprocess), content stored in a tag IC memory, or any other suitablestring.

The encoding scheme may impart session dependency to a string in anysuitable way. In some embodiments, the encoding scheme may use anerror-detection or error-correction code to impart session dependency.For example, the encoding scheme may use one or more bits of a string asan error-detection or error-correction code, such as parity bit or bits,a checksum, a cyclic-redundancy-check (CRC), or any other suitableerror-detection or error-correction code, to provide session dependency.The encoding scheme may cause one or more bits of a generated string tobe adjusted to form the error-detection or error-correction code, or maycause one or more error-detection or error-correction code bits to beadded to a generated string. In these embodiments, different codecharacteristics, such as parity, may represent different sessions. Forexample, a tag may create parity-adjusted strings such that a stringcorresponding to an even session (e.g., S0 or S2) has even parity (wherethe number of “1” values in the string including the error-detection orcorrection codes is even), whereas a string corresponding to an oddsession (e.g., S1 or S3) has odd parity (where the number of “1” valuesin the string including the error-detection or correction codes is odd).Of course, in other embodiments parity-adjusted strings corresponding toeven sessions may have odd parities and parity-adjusted stringscorresponding to odd sessions may have even parities.

In other embodiments, the encoding scheme may use one or more sessionidentifier bits to impart session dependency. For example, the encodingscheme may use a bit value of “0” to correspond to an even session(e.g., the Gen2 S0 or S2 sessions), and may use a bit value of “1” tocorrespond to an odd session (e.g., the Gen2 S1 or S3 sessions), orvice-versa. As another example, the encoding scheme may use bit valuesof “00” to indicate session S0, “01” to indicate session S1, “10” toindicate session S2, and “11” to indicate session S3. In otherembodiments, any session identifier bit values may correspond to anysession, as long as a suitably-configured reader knows or can decode thecorrespondence. The encoding scheme may add the session identifier bitsto an already-generated string, or may adjust one or more bits of analready-generated string to serve as session identifier bits.

In some embodiments, the encoding scheme may be selected based on theintended inventory session for the string or reply. For example, the tagmay use a first encoding scheme to provide session dependency for astring or reply for a first inventory session, and may use a secondencoding scheme to provide session dependency for a string or reply fora second inventory session. A suitably-configured receiving reader maythen be able to determine the session dependency of a string or replybased on the encoding scheme.

A tag may be configured to always use session-dependent replies or onlyuse such replies in certain circumstances (e.g., upon receiving acommand or upon detecting certain environmental changes). Likewise, anRFID reader or system compatible with session-dependent replies mayalways use the session dependency of session-dependent replies or mayonly use the session dependency in certain circumstances. Suchcircumstances can include received signal strength indication (RSSI)values, the types of tags in a tag population, the capabilities of tagsin a tag population, the size of a tag population, or any other suitablefactor. For example, an RFID system may use session dependency ifdetected RSSI values are relatively low or fall below a threshold. Asanother example, an RFID system may use session dependency if thepercentage or number of tags in a tag population that supportsession-dependent replies exceed or fall below a certain threshold. TheRFID system may determine the percentage or number of tags that supportsession-dependent replies based on active or passive measures. Activemeasures include sending a command that selects tags that supportsession-dependent replies, and passive measures include determiningwhether the bit value distribution of a series of received codes moreclosely corresponds to a population of tags that supportsession-dependent replies or a population of tags that do not supportsession-dependent replies.

If an RFID system does not use session dependency, it treats asession-dependent string as its corresponding, non-session-dependentversion. For example, an RFID system can treat a session-dependentrandom number as a non-session-dependent random number.

In some embodiments, an RFID system may cause suitably-configured tagsto enable or disable use of session-dependent replies. In theseembodiments, the RFID system may transmit commands that cause receivingand suitably-configured tags to begin and/or stop generatingsession-dependent replies. For example, a tag that is able to generatesession-dependent replies may initially generate session-independentreplies. The tag may then begin generating session-dependent repliesupon receiving a reader command instructing the tag to do so. In someembodiments, the tag may first authenticate the reader and/or determinewhether the reader is authorized before generating session-dependentreplies. Subsequently, the tag may stop generating session-dependentreplies upon receiving a suitable authenticated or authorized readercommand instructing the tag to do so. The RFID system may determinewhether to enable or disable use of session-dependent replies based onany suitable circumstances, such as those described above. In someembodiments, the tag may stop generating session-dependent replies upona timeout, upon generating a limited number of session-dependentreplies, or upon receiving another inventorying command. For example, areader command enabling session-dependent replies may only cause the tagto generate session-dependent replies for a limited time before the tagstops generating session-dependent replies. Thereafter, a suitablereader command may again enable the tag to generate session-dependentreplies.

RFID systems may use session dependency in a variety of applications. Inone embodiment, an RFID reader system may use session dependency toidentify the specific reader that initiated communication with a tag, asdescribed above. This reader identification may be further extended todetermine the location of RFID tags. An RFID reader system with readersor reader antennas configured to inventory tags at multiple locationsmay inventory the locations using different inventorying sessions. Forexample, the reader system may cause inventorying commands specifying afirst session to be transmitted toward a first location via a firstreader or reader antenna, while causing inventorying commands specifyinga second session to be transmitted toward a second location via a secondreader or reader antenna. The system may then use session-dependentreplies from a tag to determine whether the tag is likely located at thefirst or second location. For example, if most of the replies from thetag indicate or are based on the first session, the system may determinethat the tag is likely at the first location. If most of the repliesfrom the tag instead indicate or are based on the second session, thesystem may determine that the tag is likely at the second location.

In some embodiments, the location identification described above may befurther extended to tracking tag trajectory (e.g., the speed, direction,and path of a tag in motion). An RFID reader system configured toinventory tags at multiple locations with different inventoryingsessions may use determine tag location information (As described above)over time to determine tag trajectory. For example, an RFID readersystem configured to track tag movement through neighboring doorways orpassageways may inventory the different doorways or passageways usingdifferent inventorying sessions. When the system receivessession-dependent replies from a tag, the system may determine (a) whichdoorway or passageway the tag is likely passing through, and (b) thedirection with which the tag is passing through the doorway orpassageway.

As mentioned previously, embodiments are directed to RFID systems usingsession-dependent replies. Embodiments additionally include programs,and methods of operation of the programs. A program is generally definedas a group of steps or operations leading to a desired result, due tothe nature of the elements in the steps and their sequence. A program isusually advantageously implemented as a sequence of steps or operationsfor a processor, but may be implemented in other processing elementssuch as FPGAs, DSPs, or other devices as described above.

Performing the steps, instructions, or operations of a program requiresmanipulating physical quantities. Usually, though not necessarily, thesequantities may be transferred, combined, compared, and otherwisemanipulated or processed according to the steps or instructions, andthey may also be stored in a computer-readable medium. These quantitiesinclude, for example, electrical, magnetic, and electromagnetic chargesor particles, states of matter, and in the more general case can includethe states of any physical devices or elements. It is convenient attimes, principally for reasons of common usage, to refer to informationrepresented by the states of these quantities as bits, data bits,samples, values, symbols, characters, terms, numbers, or the like. Itshould be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities, and that theseterms are merely convenient labels applied to these physical quantities,individually or in groups.

Embodiments furthermore include storage media. Such media, individuallyor in combination with others, have stored thereon instructions, data,keys, signatures, and other data of a program made according to theembodiments. A storage medium according to the embodiments is acomputer-readable medium, such as a memory, and is read by a processorof the type mentioned above. If a memory, it can be implemented in anyof the ways and using any of the technologies described above.

Even though it is said that the program may be stored in acomputer-readable medium, it should be clear to a person skilled in theart that it need not be a single memory, or even a single machine.Various portions, modules or features of it may reside in separatememories, or even separate machines. The separate machines may beconnected directly, or through a network such as a local access network(LAN) or a global network such as the Internet.

Often, for the sake of convenience only, it is desirable to implementand describe a program as software. The software can be unitary, orthought of in terms of various interconnected distinct software modules.

According to some examples, a method for an RFID IC coupled to anantenna to operate in one of two inventorying sessions is provided. Themethod may include receiving an inventorying command specifying one ofthe inventorying sessions. If the specified session is a first session,the method may include selecting an odd parity. If the specified sessionis a second session, the method may include selecting an even parity.The method may further include generating a reply to the inventoryingcommand by generating a string for inclusion in the reply and adjustinga parity of the string to correspond to the selected parity, and sendingthe reply with the parity-adjusted string.

According to some embodiments, the string may be a random number, apseudorandom number, an algorithmically-generated value, a cryptographicvalue, and a content of an IC memory. Adjusting the parity of the stringmay include adjusting a parity bit, a checksum, acyclic-redundancy-check, an error-detection code, and/or anerror-correction code in the reply. Adjusting the parity of the stringmay include adding one or more bits to the string such that the parityof the string corresponds to the selected parity and/or adjusting one ormore bits of the generated string such that the parity of the stringcorresponds to the selected parity. The method may further includereceiving an encoding-switch command instructing the IC to begingenerating non-parity-adjusted strings, and in response to receiving theencoding-switch command generate a string for inclusion in a reply to asubsequent inventorying command and send the reply with the stringwithout adjusting a parity of the string to correspond to the selectedparity.

According to other examples, a method for an RFID IC coupled to anantenna to operate in one of multiple inventorying sessions is provided.The method may include receiving an inventorying command specifying oneof the inventorying sessions, selecting an encoding scheme based on thespecified session, generating a reply to the inventorying command bygenerating a string for inclusion in the reply and adjusting the stringaccording to the selected encoding scheme, and sending the reply withthe encoding-adjusted string.

According to further examples, an RFID IC configured to be coupled to anantenna is provided. The IC may include a transceiver configured tocommunicate with RFID readers and a processor coupled to thetransceiver. The processor may be configured to receive, via thetransceiver, an inventorying command specifying one of multipleinventorying sessions, select an encoding scheme based on the specifiedsession, generate a string for inclusion in a reply to the inventoryingcommand, adjust the string according to the selected encoding scheme,and send the reply with the encoding-adjusted string.

According to some embodiments, the string may be a random number, apseudorandom number, an algorithmically-generated value, a cryptographicvalue, and a content of an IC memory. The encoding scheme may be aparity encoding scheme, a checksum encoding scheme, acyclic-redundancy-check encoding scheme, an error-detection encodingscheme, or an error-correction encoding scheme. The method may furtherinclude, or the processor may be further configured to perform,selecting the encoding scheme by selecting a first encoding scheme ifthe specified session is a first session or a third session, andselecting a second encoding scheme if the specified session is a secondsession or a fourth session. The first encoding scheme may have an oddparity and the second encoding scheme may have an even parity. Theencoding scheme(s) may involve including a session indicator in theencoding-adjusted string. The method may further include, or theprocessor may be further configured to perform, adjusting the stringaccording to the selected encoding scheme by adding acyclic-redundancy-check and/or at least one bit to the string based onthe selected encoding scheme and/or adjusting one or more bits of thegenerated string based on the selected encoding scheme. The method mayfurther include, or the processor may be further configured to perform,receiving an encoding-switch command instructing the IC to begingenerating non-encoding-adjusted strings, and in response to receivingthe encoding-switch command generate a string for inclusion in a replyto a subsequent inventorying command and send the reply with the stringwithout adjusting the string according to the selected encoding scheme.

According to yet further examples, RFID readers and systems configuredto use session-dependent replies and methods for such readers andsystems to use session-dependent replies are provided, as describedabove.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams and/orexamples. Insofar as such block diagrams and/or examples contain one ormore functions and/or aspects, it will be understood by those within theart that each function and/or aspect within such block diagrams orexamples may be implemented individually and/or collectively, by a widerange of hardware, software, firmware, or virtually any combinationthereof. Those skilled in the art will recognize that some aspects ofthe RFID embodiments disclosed herein, in whole or in part, may beequivalently implemented employing integrated circuits, as one or morecomputer programs running on one or more computers (e.g., as one or moreprograms running on one or more computer systems), as one or moreprograms running on one or more processors (e.g. as one or more programsrunning on one or more microprocessors), as firmware, or as virtuallyany combination thereof, and that designing the circuitry and/or writingthe code for the software and/or firmware would be well within the skillof one of skill in the art in light of this disclosure.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, configurations, antennas, transmission lines, and the like,which can, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations).

Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember. Thus, for example, a group having 1-3 cells refers to groupshaving 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers togroups having 1, 2, 3, 4, or 5 cells, and so forth.

We claim:
 1. A method for a Radio Frequency Identification (RFID)integrated circuit (IC) coupled to an antenna to operate in one of twoinventorying sessions, the method comprising: receiving an inventoryingcommand, the inventorying command specifying one of the two inventoryingsessions; if the specified session is a first session, then selecting anodd parity; if the specified session is a second session, then selectingan even parity; generating a reply to the inventorying commandindicating the specified session used by the RFID IC by: generating astring for inclusion in the reply; and adjusting a parity of the stringto correspond to the selected parity; and sending the reply with theparity-adjusted string indicating the specified session.
 2. The methodof claim 1, wherein the string is one of a random number, a pseudorandomnumber, an algorithmically generated value, a cryptographic value, and acontent of an IC memory.
 3. The method of claim 1, wherein adjusting theparity of the string comprises adjusting at least one of a parity bit, achecksum, a cyclic-redundancy-check, an error-detection code, and anerror-correction code in the reply.
 4. The method of claim 1, whereinadjusting the parity of the string comprises at least one of: adding atleast one bit to the string such that the parity of the stringcorresponds to the selected parity; and adjusting at least one bit ofthe generated string such that the parity of the string corresponds tothe selected parity.
 5. The method of claim 1, further comprising:receiving an encoding-switch command instructing the IC to begingenerating non-parity-adjusted strings; in response to receiving theencoding-switch command: generating a string for inclusion in a reply toa subsequent inventorying command; and sending the reply with the stringwithout adjusting a parity of the string to correspond to the selectedparity.
 6. A method for a Radio Frequency Identification (RFID)integrated circuit (IC) coupled to an antenna to operate in one of aplurality of inventorying sessions, the method comprising: receiving aninventorying command, the inventorying command specifying one of the twoinventorying sessions; selecting an encoding scheme based on thespecified session; generating a reply to the inventorying commandindicating the specified session used by the RFID IC by: generating astring for inclusion in the reply; and adjusting the string according tothe selected encoding scheme; and sending the reply with theencoding-adjusted string indicating the specified session.
 7. The methodof claim 6, wherein the string is one of a random number, a pseudorandomnumber, an algorithmically-generated value, a cryptographic value, and acontent of an IC memory.
 8. The method of claim 6, wherein the encodingscheme is one of a parity encoding scheme, a checksum encoding scheme, acyclic-redundancy-check encoding scheme, an error-detection encodingscheme, and an error-correction encoding scheme.
 9. The method of claim6, wherein the encoding scheme comprises including a session indicatorin the encoding-adjusted string.
 10. The method of claim 6, whereinselecting the encoding scheme comprises: selecting a first encodingscheme if the specified session is one of a first session and a thirdsession; and selecting a second encoding scheme if the specified sessionis one of a second session and a fourth session.
 11. The method of claim10, wherein the first encoding scheme has an odd parity and the secondencoding scheme has an even parity.
 12. The method of claim 6, whereinadjusting the string according to the selected encoding scheme comprisesat least one of: adding at least one bit to the string based on theselected encoding scheme; and adjusting at least one bit of thegenerated string based on the selected encoding scheme.
 13. The methodof claim 6, further comprising: receiving an encoding-switch commandinstructing the IC to begin generating non-encoding-adjusted strings; inresponse to receiving the encoding-switch command: generating a stringfor inclusion in a reply to a subsequent inventorying command; andsending the reply with the string without adjusting the string accordingto the selected encoding scheme.
 14. A Radio Frequency Identification(RFID) integrated circuit (IC) configured to be coupled to an antenna,the IC comprising: a transceiver configured to communicate with RFIDreaders; and a processor coupled to the transceiver and configured to:receive, via the transceiver, an inventorying command, the inventoryingcommand specifying one of a plurality of inventorying sessions; selectan encoding scheme based on the specified session; generate a string forinclusion in a reply to the inventorying command; adjust the stringaccording to the selected encoding scheme, the encoding-adjusted stringindicating the specified session used by the RFID IC; and send the replywith the encoding-adjusted string indicating the specified session. 15.The RFID IC of claim 14, wherein the string is one of a random number, apseudorandom number, an algorithmically-generated value, a cryptographicvalue, and a content of an IC memory.
 16. The RFID IC of claim 14,wherein the encoding scheme is one of a parity encoding scheme, achecksum encoding scheme, a cyclic-redundancy-check encoding scheme, anerror-detection encoding scheme, and an error-correction encodingscheme.
 17. The RFID IC of claim 14, wherein the processor is configuredto select the encoding scheme by: selecting a first encoding scheme ifthe specified session is one of a first session and a third session; andselecting a second encoding scheme if the specified session is one of asecond session and a fourth session.
 18. The RFID IC of claim 17,wherein the first encoding scheme has an odd parity and the secondencoding scheme has an even parity.
 19. The RFID IC of claim 14, whereinthe processor is configured to adjust the string according to theselected encoding scheme by at least one of: adding acyclic-redundancy-check to the string based on the selected encodingscheme; and adjusting at least one bit of the generated string based onthe selected encoding scheme.
 20. The RFID IC of claim 14, wherein theprocessor is further configured to: receive, via the transceiver, anencoding-switch command instructing the IC to begin generatingnon-encoding-adjusted strings; and in response to receiving theencoding-switch command: generate a string for inclusion in a reply to asubsequent inventorying command; and send the reply with the stringwithout adjusting the string according to the selected encoding scheme.